Mechanical Behaviors of Electrodeposited Bulk Nanocrystalline Metals and Alloys

Nanocrystalline (NC) metals and alloys always exhibit extremely high strength but quite limited ductility. This disappointing ductility might be caused by the preparation artifacts and the weak strain hardening ability of NC materials. In order to optimize the mechanical properties of NC metals and alloys , especially to enhance their ductility, and investigate the underlying deformation mechanism, nanocrystalline Ni, dual phase Ni-Co alloy and Cu were synthesized via electrodeposition and electro-brush deposition respectively, and then a series of mechanical tests were carried out. The results show that all the materials exhibit a combination of high strength and remarkable ductility. The high strength can be attributed to the “true” nanocrystalline grain sizes ranges from 15 to 30 nm. In addition, three factors are revealed to contribute to the enhanced ductility of these materials, respectively: (a) modified deformation mode (the tensile-relaxation cycle test) for nanocrystalline Ni, (b) high strain hardening and cooperative deformation for dual-phase Ni-Co alloy, and (c) high strain rate sensitivity for nanocrystalline Cu.